NO. 1788. NORTH AMERICAN ERGASILID.^— WILSON. 347 



Vogt's brief description agrees in every detail with that of the pres- 

 ent species, and as he never published any figures the description is 

 all there is to guide us. 



Furthermore, after careful examination, the present author can not 

 agree that Hesse's Megabrachinus is at all likely to be found identical 

 with this Ergasilus. It has already been stated (p. 264) that Hesse's 

 species can not be located anywhere with certainty by reason of the 

 manifold mistakes and contradictions in his text and figures. 



Again, Vogt has tried to show that the distinctions upon which 

 Hesse founded his species are not generic distinctions at all, but only 

 specific. Be that as it may, Hesse apparently saw one thing and 

 has portrayed it clearly in his figures, which will effectually prevent 

 his species from ever belonging to the genus Ergasilus. And that is 

 a pair of good-sized maxillipeds behind the other mouth-parts. In 

 the females of Ergasilus the maxillipeds are entirely wanting; if 

 there is any truth in Hesse's figure, therefore, the specimens he was 

 trying to portray certainly did not belong to the genus Ergasilus. 

 He does not even mention the appendages in his text, so that we 

 can get no help from that source. We can easily understand how 

 he might omit some descriptions — no author ever describes all the 

 details of his figures. But it would hardly be reasonable to suppose 

 that he deliberately drew a pair of appendages which did not exist. 

 We may safely conclude then that his " MegahracMnus" will never 

 prove to be an Ergasilus, and may thus with greater assurance restore 

 Vogt's original name for the present species. 



Genus THERSITINA Norman. 



Thersites, Pagenstecher, 1861; Ergasilus, Kroyer, 1863, and Gadd, 1901; Ther- 

 sitina, Norman, 1906. 



This genus was originally described by Pagenstecher in 1861 under 

 the name Thersites, borrowed from the Iliad. His description was 

 fairly good, but he acknowledged that the mouth-parts were "indis- 

 tinct" and presented no details with reference to the swimming legs, 

 both of which are essential for the determination of specific distinc- 

 tions. 



He found three pairs of mouth-parts, which he designated as max- 

 illse and first and second maxillipeds, respectively; the mandibles he 

 believed to be inside the mouth, where they could not be seen. But 

 mandibles inside the mouth would make of the latter a sort of pro- 

 boscis, and Pagenstecher distinctly states that nothing of the sort is 

 formed. Hence we can get no satisfactory data from his description. 



Two years later (1863) Kroyer described the same species from the 

 same host, but called it Ergasilus gasterosteus. He found what he 

 openly designated as a rostrum or proboscis at the mouth, but he 

 did not have the courage to name definitely any of the mouth-parts. 



